This invention pertains to a servo mechanism for intensifying the braking power of a motor vehicle.
Presently so-called servo brake systems are being installed in nearly all motor vehicles. These servo brake systems intensify the pressure exerted on the brake pedal by the driver to a sufficiently high brake pressure. The auxiliary power necessary for this purpose is gained from diverse systems. For instance there are hydraulic power brakes for the operation of which a pump for the fluid has to be available. In other cases the vacuum in the intake manifold of the motor is utilized. However, vacuum assisted systems are not easily utilized in vehicles with fuel injection.
From DE-OS No. 27 58 644 a brake unit is known, in which an electric motor serves as an accessory drive. Via a friction clutch and an overunning clutch the electric motor drives a pinion serving as a servo member. The pinion mates with a push rod partly formed as a rack which leads from the brake pedal to the brake master cylinder. The friction clutch may be regarded as a pressure-sensitive element. The greater the pressure which presses the two clutch halves together, the greater is the torque which can be transmitted to the servo member via the clutch, and the larger is the counterforce against which the push rod can still be adjusted. If at a given value of the frictional connection between the two clutch halves this counterforce is exceeded by a certain amount, there occurs a clutch slippage and the push rod is not further adjusted.
The support axes of the servo member, of the clutch disks and the motor shaft of the known device extend vertically to the push rod. The consequence is that the clutch can only be controlled from the brake pedal via a complicated lever power transmission which requires significant space. During braking big transverse forces appear in the bearing of the pinion and in one clutch half which result in significant bearing-friction. This bearing-friction is also noticeable, when by increasing the pressure exerted onto the brake pedal, the pinion and the one clutch disk are somewhat displaced in axial direction. Because of the bearing-frictions which appear in the lever system, an extremely high hysteresis between brake line pressure and brake pedal pressure is created.